Field of the Invention
The present invention relates to a cylinder head gasket which is installed while being sandwiched between a cylinder block and a cylinder head in an internal combustion engine, and a method of manufacturing the cylinder head gasket.
Description of the Conventional Art
There has been conventionally known a tabular metal cylinder head gasket 51 which is schematically shown in FIG. 6. A desired number of bore holes 52 having a circular plane surface are provided at a position which is lapped over a combustion chamber in a cylinder block in correspondence to the number of the cylinders, on a plan of the cylinder head gasket 51, and a surface pressure generation portion 55 is provided at a position (a partition wall overlapping portion) 53 which is lapped over a partition wall between a combustion chamber in the cylinder block and a water jacket portion, the surface pressure generation portion 55 being constructed by a three-dimensional shape such as a bead or a step which surrounding the bore holes 52.
A position (a W/J overlapping portion) 54 lapped over the water jacket portion in the cylinder block is drawn by a dotted line in FIG. 6. The partition wall overlapping portion 53 is provided between the W/J overlapping portion 54 and the bore hole 52, and the surface pressure generation portion 55 shown by a single-dot chain line on the drawing is provided in the partition wall overlapping portion 53. Further, a surface pressure generation portion 55 is provided in an outer side of the W/J overlapping portion 54 in order to prevent a cooling water in the water jacket portion from leaking to an external portion of the cylinder block.
The surface pressure generation portion 55 provided in the partition wall overlapping portion 53 is provided as a seal for bore which seals so as to prevent high-pressure gas in the combustion chamber from leaking, and is also provided as a seal for water which seals so as to prevent the cooling water in the water jacket portion from leaking to the bore side. The three-dimensional shape of the surface pressure generation portion 55 includes a shape (a bead type) which is constructed by a bead, and a shape (a stopper type) which is constructed by a shim welded (or folded-back) stopper and forms a step on the basis of a thickness difference.
Further, since the surface pressure generation portion 55 is provided as the seal for bore and the seal for water as mentioned above, the surface pressure generation portion is frequently formed as a double seal line. An inside single-dot chain line in FIG. 6 indicates a first surface pressure generation portion 55A which serves as the former seal for bore, and an outside single-dot chain line indicates a second surface pressure generation portion 55B which serves as the latter seal for water.
The first surface pressure generation portion 55A is formed so as to individually surround a plurality of bore holes 52, and is formed concentrically in relation to the bore hole 52 having the circular plane. The second surface pressure generation portion 55B is formed so as to collectively surround a plurality of bore holes 52, however, is formed concentrically in relation to the bore hole 52 having the circular plane, in the same manner as that of the first surface pressure generation portion 55A in the other areas than intermediate areas between the adjacent bore holes 52 to each other. Further, the partition wall overlapping portion 53 provided with these first and second surface pressure generation portions 55A and 55B is formed concentrically in relation to the bore hole 52 having the circular plane, and is formed into an annular area having a fixed width (a diametrical width) w. Further, since the first and second surface pressure generation portions 55A and 55B are arranged so that their intermediate positions are fixed positions in a width direction of the partition wall overlapping portion 53, and the partition wall overlapping portion 53 is a position which is lapped over the partition wall, the first and second surface pressure generation portions 55A and 55B are arranged so that their intermediate positions are fixed positions in a thickness direction of the partition wall.
In the meanwhile, in the case that the cylinder head gasket 51 is assembled between the cylinder block and the cylinder head and is fastened by bolts, there is generally generated a so-called bore deformation that the cylinder block is deformed by a reaction force of the surface pressure generation portion 55 which is generated in connection with a bolt fastening axial force input. In this regard, it has become a great problem to reduce a friction of an engine, that is, reduce the bore deformation on the basis of demands for improving a fuel consumption in recent years.
In order to reduce the bore deformation, it can be thought to lower a spring constant of the bead type, and reduce an amount of step of the stopper type.
However, the improvement of fuel consumption is demanded more and more severely. Accordingly, if the bead spring constant is further reduced or the amount of step is reduced for further lowering the bore deformation, the sealing surface pressure is lowered more and more, and there is a risk that a sealing performance is adversely affected.